531 research outputs found
Rigid surface operators and S-duality: some proposals
We study surface operators in the N=4 supersymmetric Yang-Mills theories with
gauge groups SO(n) and Sp(2n). As recently shown by Gukov and Witten these
theories have a class of rigid surface operators which are expected to be
related by S-duality. The rigid surface operators are of two types, unipotent
and semisimple. We make explicit proposals for how the S-duality map should act
on unipotent surface operators. We also discuss semisimple surface operators
and make some proposals for certain subclasses of such operators.Comment: 27 pages. v2: minor changes, added referenc
Wave-growth associated with turbulent spot in plane Poiseuille flow
A kinematic wave theory is used to investigate the cause of the rapid growth of waves observed at the wingtip of turbulent spot in plane Poiseuille flow. It is found that the qualitative behavior of the wave motions is well described by Landahl's breakdown criterion as the wave selection procedure. The predicted wave number, wave angle, and phase velocity are in agreement with those values obtained in a direct simulation
Turbulence characteristics inside a turbulent spot in plane Poiseuille flow
In wall-bounded shear flows the transition to turbulence through localized disturbances goes through a pattern starting with a development of shear layers. The localized normal velocity fluctuations induce normal vorticity through the lift-up effect. These shear layers become unstable to secondary disturbances, and if the amplitudes of the disturbances are large enough, a turbulent spot develops. Investigations of the spot in boundary layers has shown that the turbulent part of the spot is very similar to a fully developed boundary layer. Wygnanski et al. (1976) showed that the mean profile at the center-symmetry plane has a logarithmic region and Johansson et al. (1987) showed that both the higher-order statistics and flow structures in the spot were the same as in the corresponding fully developed flow. In what respects the turbulence inside the Poiseuille spot is similar to fully developed turbulent channel flow is studied. The numerically simulated spot is used, where the characteristics inside the spot are compared to those of the wave packet in the wingtip area. A recent experimental investigation of the velocity field associated with the Poiseuille spot by Klingmann et al. is used for comparison
The Self-Dual String and Anomalies in the M5-brane
We study the anomalies of a charge self-dual string solution in the
Coulomb branch of M5-branes. Cancellation of these anomalies allows us to
determine the anomaly of the zero-modes on the self-dual string and their
scaling with and . The dimensional reduction of the five-brane
anomalous couplings then lead to certain anomalous couplings for D-branes.Comment: 13 pages, Harvmac, refs adde
Large scale flow around turbulent spots
Numerical simulations of a model of plane Couette flow focusing on its
in-plane spatio-temporal properties are used to study the dynamics of turbulent
spots.Comment: 16 pages, 6 figure
A class of six-dimensional conformal field theories
We describe a class of six-dimensional conformal field theories that have
some properties in common with and possibly are related to a subsector of the
tensionless string theories. The latter theories can for example give rise to
four-dimensional superconformal Yang-Mills theories upon
compactification on a two-torus. Just like the tensionless string theories, our
theories have an -classification, but no other discrete or continuous
parameters. The Hilbert space carries an irreducible representation of the same
Heisenberg group that appears in the tensionless string theories, and the
`Wilson surface' observables obey the same superselection rules. When
compactified on a two-torus, they have the same behaviour under -duality as
super Yang-Mills theory. Our theories are natural generalizations of the
two-form with self-dual field strength that is part of the world-volume theory
of a single five-brane in -theory, and the theory can in fact be
seen as arising from non-interacting chiral two-forms by factoring out the
collective `center of mass' degrees of freedom.Comment: 8 pages. More pedagogical presentation, added section on relationship
to d = 4 Yang-Mills theor
Diffeomorphisms and Holographic Anomalies
Using the relation between diffeomorphisms in the bulk and Weyl
transformations on the boundary we study the Weyl transformation properties of
the bulk metric on shell and of the boundary action. We obtain a universal
formula for one of the classes of trace anomalies in any even dimension in
terms of the parameters of the gravity action.Comment: 12 pages, harvma
Renormalization Group Flows from Five-Dimensional Supergravity
The use of gauged supergravity as a tool in studying the
AdS/CFT correspondence for Yang-Mills theory is reviewed. The
supergravity potential implies a non-trivial, supersymmetric IR fixed point,
and the flow to this fixed point is described in terms of a supergravity kink.
The results agree perfectly with earlier, independent field theory results. A
supergravity inspired -function, and corresponding -theorem is discussed
for general flows, and the simplified form for supersymmetric flows is also
given. Flows along the Coulomb branch of the Yang-Mills theory are also
described from the five-dimensional perspective.Comment: 12 pages, 3 figures; Latex, ioplppt.sty, iopl12.sty, epsf.sty.
Contribution to Strings `9
- …